Did you check in the catalog, or try the site map? Maybe someone has already borrowed it. Or maybe you might have made a tiny spelling mistake when you typed in the URL? You could always try a site search, or maybe have another attempt at typing in the URL.
Maybe the file might be in the returns chute, or waiting to be reshelved.
We can check to see if it's been mishelved. That sometimes happens on large websites, or if someone has been just a little careless.
Still can't find it? Have you considered using a similar file? Or another title?
We can try to order you in similar file from another website. That could take a couple of days to a couple of weeks, depending on its availability.
Oh, you didn't want to wait that long? Have you tried kicking the *#&*^$%@^#%& out of your computer?
It won't help find the file, but it sure will make you feel a lot better. At least until you get the repair bill ...